Companies that stockpiled trillions of dollars offshore free ofU.S. income tax may get one last break before paying up—providedtheir fiscal years don't follow the calendar year.

A timing quirk in the tax overhaul that President Donald Trumpsigned last month may be good news for companies such as Apple,Microsoft and Cisco, all of which began their fiscal years beforeJan. 1. Firms including Alphabet, Amgen and General Electric—withfiscal years that began on Jan. 1—appear to be shut out of thebenefit.

Apple alone, which disclosed an offshore cash hoard of $252billion as of Sept. 30, may be able to lop more than $4 billion offa future tax bill, according to Stephen Shay, a tax and businesslaw professor at Harvard Law School who wrote about what he calledthe “potential loophole” last month. He characterized the boon as aside effect of the speed with which congressional Republicanspassed their tax bill.